The K39 is designed to use all the options available to the Stressemann, with the best being the LVL 115 twin 20"/48 KL-00.

The LVL 100 20"/48 SK C/40 would be a workable second option, while the LVL 110 18"/45 SK C/34 are still useable as well, but suboptimal due to issues that were never fixed.